A 64-bit instruction set is about more than just the size of a pointer. A 64-bit CPU has 64-bit general-purpose registers, and it has versions of arithmetic an

A 64-bit instruction set is about more than just the size of a pointer. A 64-bit CPU has 64-bit general-purpose registers, and it has versions of arithmetic and logic instructions operating on these. Because 32 bits is enough for most purposes, instructions must also have a variant operating only on the lower half of the registers, the upper half being either ignored or sign-extended from the lower as appropriate. This makes the CPU core a fair bit more complicated, meaning larger silicon footprint are higher power consumption. I agree a 64-bit ARM is unlikely in the immediate future. Extending the physical address space beyond 4GB is possible without any changes to the instruction set. See x86 PAE for an example. In short, the MMU translates a 32-bit virtual address into a wider physical address. This allows running multiple processes with a total memory requirement of more than 4GB. As the vast majority of applications never need more than 4GB of virtual space anyway this isn't much of a restriction in practice. I reckon this kind of thing is something we might see in an ARM core relatively soon, at least if they keep growing in the netbook market.